1. Field of the Invention
The present invention relates to a navigation system to be mounted in a motor vehicle.
2. Description of Background Information
Recently, on-board navigation systems (navigation system to be mounted in a vehicle) for motor vehicles are developed, in which map data in digital form is stored in a memory and a map of a region around the present location of the vehicle is displayed on a display by reading-out from the memory map data of the region having a given area including the present location of the vehicle, while recognizing the present location of the vehicle, and the location of the vehicle itself is automatically indicated on the map being displayed.
In such navigation systems, use of a memory device is indispensable since the map data in numerical form is required, and moreover a memory device of a large memory capacity becomes necessary since the map data has a considerable data amount in order to satisfy various requirements. One the other hand, for displaying a map of a region around the vehicle on the display on the basis of data in numerical form for example, a semiconductor memory of a large capacity as well as a display unit which is operable at fast speeds become indispensable.
Therefore, the electric power consumption of the navigation system having these devices or units becomes necessarily large. However, since the capacity of electric power supply in a vehicle is limited, it is desirable to provide a measure for reducing the electric power consumption of the navigation system.